How to upscale an image to 300 DPI and 10,800 x 7,200 pixels on Mac?

I can see you've scaled this image up quite a ways to get it to 24" x 36" at 300 dpi. The edges are soft and pixelated.

Random clip of the overall image:

Granted, this is viewing it 1:1, which is much larger than actual size. In Photoshop on my monitor, viewing a 300 dpi image at 36% is actual size. Then it's a very good indication of what the print will actually look like. Still kind of soft, but not bad.

The main problem with the image is you have no color profile attached to it. There's no way for the vendor to know what you used, and it can greatly change the output color you're expecting if they guess wrong.

I can make it match in Photoshop to how the image displays in Safari by choosing to assign sRGB as shown above, but that's only because Safari defaults to applying sRGB on the fly when an object has no profile attached to it.

This is far more important that it may sound. Here, I made a copy of your image and opened one with sRGB assigned, and the other Adobe RGB. Neither of which you may be using.

Drastically different color from the same image. This is the conundrum your output service will be in. And they may not ask what your intent was. They will simply apply sRGB, and you'll get what you get.

You can do what you want with the free Affinity suite of apps. In Affinity use this menu option:

and then resize like this: change the pixels to what you want and then change the DPI to 300:

(10,800 dots) ÷ (300 dots/inch) = 36 inches.

If you're sending this to a printer or to a printing service, it doesn't matter what Preview says is the height and width in inches-- all that counts is that the resolution is high enough to justify the size and satisfy the printer. The printer or service will make it the right number of inches.

Can you tell us what you are really trying to do? Apparently you originally have about 3000 pixels across-- is that right? 72 dpi is typical for computer screens. 300 dpi is good for text on paper held at normal reading distance. Generally you don't view 36 inch pictures at normal reading distance, and photographs are a bit more forgiving than text, so I wonder why you need such resolution. I have a number of photographs up on walls with less than 300 dpi, and they look great if you don't use a magnifying glass. Keep in mind that adding pixels is tricky, since just sticking in new pixels in doesn't make the picture look better.

Change the drop down menu that currently says inches to pixels. Set the size in the width or height. The other will follow proportionately. Change 72 to 300. Click OK.

Any idea why?

As Yer_Man noted, image apps don't really know what an inch is. And it's more like, don't care. If you copy an image and set the resolution on the first to 10 and the other 10,000 (without resampling so each maintains the number of pixels it started with), they're going to display the same on screen.

Resolution is only important to an output device. The resolution tells the device how many linear pixels to user per inch. 300 is standard for most printing needs. Higher doesn't result in a visually sharper image. Lower is okay, depending on how far you're viewing the print from. 200 dpi works well enough for a large print you're standing back a ways from, but will look slightly pixelated on a small print you're holding (like a 4"x6" or 5"x7").

Places you send images to normally require 300 dpi because that's what their devices default to, and expect. If you send images in as anything other than 300 dpi, then they'll scale your image(s) to that resolution anyway so they can print it. This includes places like Mpix where their web site will let you pick sizes that are larger than you have pixel data for at 300 dpi. But all that means is they think the image can be scaled up larger than you have data for and maybe not notice the fuzzier result. It will still be scaled to 300 dpi whether the image is going up or down from its native size.

Some weirdness going on here. Photoshop insists there is no tagged profile, but Preview shows that sRGB is attached.

I ended up using the Extract AppleScript in the ColorSync folder to confirm, and yes, sRGB is part of the image. Turns out your image has an Alpha channel attached. If I simply save the file again out of Preview and turn the Alpha check box off, then PS recognizes the profile.

Forget CMYK. The image is RGB. Even on canvas, the printer will use a Giclée or other wide gamut inkjet printer, which has far more color range and gamut than CMYK. If you have a print made, that will be on color photo paper. Also far more color than CMYK can muster.

sRGB ("stupid" RGB) is the most useless RGB profile in the world. Put another way, it's the least common denominator profile. Bottom of the barrel. Last resort. We have Microsoft and HP to thank for pushing this crummy color space on everyone as the "standard". The purpose? It was meant to account for the color range of consumer monitors at the time. Many of those old CRTs couldn't even display sRGB. This is now completely outdated. It's difficult to find even a somewhat inexpensive monitor that can't display Adobe RGB's range, or close to it.

Otherwise, what you have is ready to go. It's already 300 dpi at 36"x24", and it has an embedded profile. The only thing you can't control is color intent. I trade off between Mpix and Bay Photo, depending on what I want done. In both cases, they always use Perceptual, whether you want them to or not. I've called both and asked them this, and I do wish they would use Relative Colorimetric.

Preview doesn't really know what an inch is. Are you printing this? Set your dimensions in the print dialogue.

I was going to add: (10,800 dots) ÷ (300 dots/inch) = 36 inches. When I tried this it gave me the right results.

The only time I've done this is to send it to a printing service that wouldn't print at a lower resolution (than 150 dpi, I think.) It was to satisfy them-- adding pixels didn't make the picture any better.

Michael Williams10 wrote: … I want to send it to a printer to print on metal. I think. Or maybe canvas.

I don't click on links from users, but from what you've said, your results got from following Kurt Lang's instructions will be fine.